The present invention relates to a press roll for treating web material, and preferably for removing water from a web of fibers. The press roll forms a press nip with a counter roll. The press roll has an elongate support member which is either stationary or rotatable. The press roll has an endless flexible, liquid-impervious press jacket which is disposed on the fixed or rotatably mounted support member extending through the jacket. The invention concerns the clamping of the lateral ends of the press jacket and to the design of those ends.
According to Federal Republic of Germany DE-OS No. 19 23 784, if a stationary rather than a rotary support member is present, the flexible press jacket slides over the support member in the region of the press nip when the support member presses the press jacket against the counter roll. For this purpose, as taught in Federal Republic of Germany DE-OS No. 31 02 526, a press shoe which is movable in the radial direction is provided on the support member, with the press jacket sliding over that shoe. The slide surface of the press shoe is usually concave in shape, corresponding to the curvature of the counter roll. As a result, the press nip has a certain length in the direction of travel of the web, i.e. an extended press nip is formed. The cross sectional shape of the support member may be any desired shape, for instance rectangular, tubular or I-shaped.
If the support member is rotatably mounted rather than fixed, and if it has the shape of a circular-cylindrical rolling body, then when the support member presses the press jacket against the counter roll, the support member rolls in the region of the press nip against the inner side of the press jacket (as shown in Federal Republic of Germany DE-OS No. 15 61 674). In the construction in the German application the press jacket is perforated. The press roll of the invention, in contrast, always has a liquid-impervious press jacket, since its inner side must, as a rule, carry a film of lubricant, and none of the lubricant must penetrate outward from the inside of the press roll. Otherwise, there would be the danger of contamination of the web which is to be treated.
Known press rolls have on each end of the support member a press jacket support element which is in the form of a disk which is mounted for rotation. According to Federal Republic of Germany DE-OS No. 19 23 784, each of the two ends of the press jacket has a radially inwardly deformed, spatially curved, edge zone which has a bead, in the manner of an automobile tire. This edge zone is attached by means of a clamping flange to one end of the jacket support element. The attachment is liquid-tight, i.e. the press jacket lies against the jacket support element in the region of an end annular sealing surface. the edge zone having the bead extends relatively far toward the axis of the roll, i.e. the inner circumference of the flexible press jacket is substantially smaller in the region of the end opening than in the region of the press zone. This makes it difficult to pull the press jacket over the support member and over the elements provided on the support member for the guidance of the press jacket, for instance, guide rolls in the case of the known press roll.
In the press roll of the invention, the press jacket, as known from Federal Republic of Germany DE-OS No. 31 02 526, is preferably made of a reinforced, relatively hard plastic, for instance polyurethane, and it preferably has a relatively stiff fabric reinforcement. Press jackets of this construction are preferred, particularly in roll presses having extended press nips, since they withstand the high frictional stresses in continuous operation relatively well. However, the liquid-tight connection of such a press jacket to the jacket support element, preferably jacket support disks, affords difficulties. It has been attempted, corresponding to the construction in Federal Republic of Germany DE-OS No. 15 61 674, to fasten the two ends of the flexible press jacket, not to an outer end side, but to an outer cylindrical circumferential side of the jacket support disks. The advantage of this method is that deforming the ends of the press jacket in the direction toward the axis of the roll is not necessary. A disadvantage, however, is that the required liquid tightness can be obtained only at great expense. It is very difficult to manufacture the inner circumference of a press jacket in such a way that it exactly fits the outside diameter of the jacket support disks. This is quite expensive because the press jacket must be periodically replaced by a new one because of wear.